5.D
6.B
7.C
8.D
III
1.D.TO PLAY-PLAYING
2.C.USED TO SINGING-USED TO SING
3.C.FOR-BY
4.C.TO NOT-NOT
IV
1.It's very important to keep the enviroment clean.
2.I haven' t spoken to her for 3 years.
3.She told me not to forget to send my parentsmy regards.
4.Trung was given a microcomputer by his parents on his birthday.